Oversize supply and return for possible future expansion

eddo

I'm replacing an old cast iron 80,000BTU boiler with a Rinnai E50c in our 1840 house that we've been insulating and replacing windows in. The old system has 2 zones with zone valves. I'm changing it to a single zone with a low loss header and added circ pump (the Rinnai has a built-in circ pump that'll be used as the primary pump). I have one room with a fireplace, with a wood stove insert, that's never had hydronic heat in it, and I may add a zone there sometime down the road, not sure yet. The old boiler has 1" supply and return piping to the 3/4" zones. I had planned to just do a 3/4" supply and return for the new single zone, but with the possible expansion I'm wondering if it might be better to do 1" now? The new boiler is hung on the wall only about 5' from the possible future zone, so going 1" from the low loss header supply to just past the circ pump would be easy, then for now I could run 3/4" from there to the new single zone. If I add the 2nd zone later I could tie in right past the circ pump and have the 2 zones split there, with new zone valves. The return could be the same, 1" close to the boiler, with the 2 zones merging there. I would have to buy a 1" flange for the pump, a 1" Spirovent and dirt trap, and a few 1" ball valves for the area right near the boiler (system flushing and purge station). Does it make sense to spend what seems to be just little bit extra now for the larger 1" components? Or do you think I'm missing something here?

Jamie Hall

Your call -- but the bigger pipes in that situation wouldn't hurt anything. It's sort of pay now or pay -- maybe -- later.

hot_rod

with a 50K boiler, 47K DOE output, really no need to use 1”. Unless you plan on a larger boiler someday

eddo

Thanks for both responses. Maybe I wrongly assumed that if I'm feeding a 3/4" loop for one zone, that adding a 2nd 3/4" loop would mean having a 1" supply and return line to the branch of those loops. Isn't that typical?

Zman

From the point of view of btu transportation, your 3/4" pipe will move 64,000 btus at a 20 degree delta t and 6.4 gpm (4 ft/sec) so 3/4" is sufficient.

From the general description of your system, it sounds like you may get more even distribution with a 1" pipe feeding (2)-3/4" pipes. It certainly won't hurt anything.

hot_rod

Ideally you would define and calculate the piping including heat emitters in the circuit(s).

The amount of BTU that you need to deliver to each loop, the ∆T you plan on running, then calculate the piping to get a pressure drop for the system. The circulator sizes to the load (but/hr.) and the resistance, pressure drop of the system.

The quick answer is 3/4 will be adequate, an exact answer regarding the hydraulics of the actual system would involve some number crunching.

If the cost to upsize all the components is in the wheelhouse, no harm in upsizing.

eddo

Thanks all!